Alluvial and fluvial fans on Saturn's moon Titan

Alluvial and fluvial fans, landforms that record storage and transport from uplands to depositional basins, are found on Saturn’s moon Titan. At its location in the solar system, this body has significantly colder... [ view full abstract ]

Alluvial and fluvial fans, landforms that record storage and transport from uplands to depositional basins, are found on Saturn’s moon Titan. At its location in the solar system, this body has significantly colder temperatures, slower rates of processes and vastly different fan materials than Earth. The working fluid is methane while sediments are composed of water ice and organics derived from atmospheric processing of methane. Images of Titan’s surface obtained by the Cassini spacecraft’s Synthetic Aperture Radar (SAR) reveal morphologies, roughness, textural patterns and other properties consistent with fan analogues on Earth. Fans emerge from narrow channels and broaden across regions known to have decreasing regional slopes. In some areas, the slope is not known but can be inferred from fan morphologies. The observed fan characteristics on Titan reveal some regions of high relative relief and others with gentle slopes over hundreds of kilometers, exposing topographic variations and influences on fan formation. There is evidence for a range of particle sizes across proximal to distal fan regions, from ~2 cm or more to fine-grained, which reveal details of sedimentary processes. Some features are best described as alluvial fans, which implies their proximality to high-relief source areas, while others are more likely fluvial fans, drawing from larger catchment areas and frequently characterized by more prolonged runoff events. Titan’s overall relief is relatively low compared with Earth, but regional and local differences exist and are emphasized by fans. Continued analysis of topographic data across Titan, where available, will allow more characterization of fan properties. These studies may help establish whether alluvial fans on Titan are related to passive dismantling of local topographic highs or tied to continued clastic shedding from relief sustained by long-term tectonics. The range of sedimentary and other processes modifying Titan's landscape makes it difficult to detect indications of tectonics, which are only revealed in the presence of mountain chains and control of river networks. Thus, alluvial fans may provide a new window into tectonism on Titan. The presence of fans corroborates the vast liquid storage capacity of the atmosphere of Titan and resultant episodic behaviour. Fans join the growing list of landforms on Titan derived from atmospheric and fluvial processes similar to those on Earth, strengthening comparisons between the two planetary bodies.